In 2020, I’ve discovered Matthew Walker’s book, ‘Why we sleep’ and it really stayed with me and, in a way, it shocked me to find out how important our sleep (and the quality of it) is for our good health. Reading this book about the neuroscience of sleep made me buy myself a smartwatch that can analyse sleep 😊. The book also helped me understand how sleep functions, what it is helpful for, etc.
And the book starts with a very interesting and logical argument: all beings’ sleep. And we all know that when we are asleep, we are very vulnerable. And we also know that mother nature is very wise and it wouldn’t oblige us to be vulnerable for a good amount of time every day (night) if sleep wouldn’t be important. So, if sleep wouldn’t have been useful for survival and natural selection, during the hundreds of millions of years of evolution, nature would have discontinued sleep. At least for some species. But there are no species that do not sleep and then, starting from this idea, sleep really must be something very useful and healthy for us. Going deeper, there are some elements that make sleep a very useful tool for stress reduction and resilience building.
How much sleep do we need and what are the benefits?
First, as an adult, getting a minimum of 7h, but preferably 8h of sleep each night, is something very useful from two perspectives: first, during sleep, the secretion of stress hormones cortisol and adrenalin is inhibited, which means that our body is getting cleansed of stress hormones and of their negative effect on us.
Second, during sleep, our pulse drops significantly, to the low 50s, versus the 60-80s beats/minute that might be normal during the day. Secondly, the frequency of respiration decreases. These are all signs of parasympathetic branch activation. The parasympathetic branch of our autonomic nervous system is associated with the rest and digest phase when the body recovers and rebuilds. It is the antagonistic branch to the sympathetic system, which is leading us in fight or flight stress responses.
Another thing that Matthew Walker mentioned in the book is that sleep is a key element to recover after trauma or prolonged stress. On the one hand, this is because of the things I mentioned just beforehand, on the other, is that our explicit memory is consolidated during sleep. And, when we sleep, if during the day we’ve been through some stressful experiences, which annoyed us, made us bathe in cortisol (e.g. had a bad moment with the boss or with a colleague, our kid didn’t listen to reason, etc.) and we went to sleep with this cortisol in our body… well, during our sleep, cortisol is eliminated from our bodies and, even cooler, the memory of what happened during the day will be imprinted in our memory, but without the emotional print – so without the cortisol/adrenaline involved.
Sleep is like free therapy
This is why, Matthew Walker explains very nicely that, in fact, sleep is like free therapy.
You might have noticed yourself: you’re going to bed really annoyed or furious because of something that happened earlier in the day. And, without anything changing in that situation that caused our distress, the second day you wake up in a much better state… The explanation is that the conscious memories will remain with us, with the discussion/fight/whatever did not work, but the emotional print of it will disappear. The hippocampus, when it’s encoding the explicit memory, loses the emotional imprint given by cortisol and adrenaline (or, better said, by the amygdala, as this one is calm during sleep).
This is why we also say that good sleep makes for good advice because without the sympathetic branch activated (so without the stress hormones in our bodies) we can actually use our cognitive capacities and make better decisions – we’re using our Rider to make decisions, not our Elephant.
Lack of sleep – what happens then?
Now, what is also worth discussing is that lack of sleep leads to increased blood pressure, inflammation in the body, reduced emotional regulation and cognitive function decline.
That is because during sleep is the only time that the brain can clean itself, get rid of residues… it’s like it’s the night shift (and only shift) to take care of repair and maintenance operations for the brain. This function is undertaken by the brain’s glial cells, forming the glymphatic system. This system drains waste products (including stress hormones) from the brain with the help of the cerebrospinal fluid, a clear liquid surrounding the brain and spinal cord, which moves through the brain along a series of channels that surround blood vessels.
Therefore, my recommendation for you is to sleep at least 8h every night (7h if you don’t have a choice). Walker states a very long list of issues that appear if we sleep under 7h/night and believe me… it’s scary!
So, if you’ve heard people saying that ‘I can do with 4h or 5h a night’, ‘sleeping is for losers’, etc, if you care about them, recommend them to read Walker’s book. He even gives examples of public figures who had said they’ve had years of only sleeping that little amount and how, at old age, they suffered from various brain-related diseases: Alzheimer’s and other types of dementia being at the top….
Now: what about too much sleep? Is there a maximum threshold?
In his book, Walker doesn’t mention if there is a maximum threshold of hours of sleep per night for adults, but what I can say is that if you repeatedly feel like you need to sleep longer than 8h, that means that you have a sleep debt that accumulated because of sleepless nights or for periods when we did not get enough sleep. He says it very clear that there is no such thing as ‘recovering sleep’. That is a myth. If you sleep only 6-7h during the week, you won’t ‘recover’ from that lost sleep by sleeping longer at the weekend. And this is based on studies that measured brain activity in people.
In the case of teenagers, given that their brain is still building and forming itself (tip: the neocortex is developing until mid-twenties), they actually need between 11 and 12h of sleep every night. So, the idea of having teenagers starting school at 7 or 8 am, as I have experienced it in my past, it’s a total disaster for the brain development of a kid. It is a lot better to start classes later so that teenagers have a chance to actually sleep 10 to 12 h per night. In the end, it’s not that they are lazy and this is why they sleep a lot, it’s simply what their brain and body need to develop correctly.
I hope you found this article useful and now… please go to sleep 😊.
Stay healthy, stay happy, stay safe,
Magda.
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Walker’s book is on my to-read list for a while. Now it became even more interesting.
Thank you for sharing, Magda!
Glad to hear that, Daniel! Yes, it’s really interesting.
I must say, some of those statistics really scared me… I never thought sleep was so important.
I hope you’ll enjoy reading it.